Electrolytic process for depositing a graduated layer on a substrate, and component

ABSTRACT

This invention relates to an electrolytic process for the deposition of a graduated layer on a substrate. The process includes depositing a composite material having a first constituent and a second constituent forming a graduated layer on a substrate, introducing the substrate into an electrolyte for a period of time, varying the fist and second constituents of the electrolyte during the period of time to achieve the graduated layer, and using a current/voltage pulse for the electrolytic deposition such that an optimized deposition of the constituents occurs.

The invention relates to an electrolytic process for the deposition of a graduated layer on a substrate as claimed in claim 1 and to a component produced using this process as claimed in claim 21.

There are various known processes for applying layers to a substrate. These include, for example, plasma spraying, electroplating or evaporation coating, inter alia.

An article by G. Devaray in Bulletin of Electrochemistry 8 (8), 1992, pp. 390-392 entitled “Electro deposited composites—a review on new technologies for aerospace and other field” gives an overview of processes for the electrochemical deposition of layers.

DE 101 13 767 A1 discloses an electrolytic plating process.

DE 39 43 669 C2 discloses a process and an apparatus for electrolytic surface treatment in which the mass fractions used for coating are intimately mixed by vibratory motion and/or rotary motion, so that a uniform electrolytic layer is deposited.

Further electrolytic processes for coating are known from GB 2 167 446 A, EP 443 877 A1 and from the article by J. Zahavi et al. in Plating and Surface Finishing, January 1982, pp. 76 ff. “Properties of electrodeposited composite coatings” in which undissolved particles in the electrolyte are used to also deposit these particles in the layer.

In Electrochemical Society Proceedings Vol. 95-18, pp. 543 ff. von Sarhadi et al. entitled “Development of a low current density electroplating bath . . . ”describes the use of baths which contain cobalt, nickel or iron compounds.

U.S. Pat. No. 6,375,823 B1 describes an electrolytic coating method which uses an ultrasound probe.

DE 195 45 231 A1 describes a process for the electrolytic deposition of metal layers in which a pulsed current or pulsed voltage method is used. However, this is employed only in order to reduce aging phenomena in deposition baths.

U.S. 2001/00 54 559 A1 discloses an electrolytic coating process which uses pulsed currents in order to prevent the undesired evolution of hydrogen during electrolytic coatings of metals.

DE 196 53 681 C2 discloses a process for the electrolytic deposition of a pure copper layer in which a pulsed current or pulsed voltage method is used.

DE 100 61 186 C1 describes a process for electrolytic deposition in which periodic current pulses are used.

In the article entitled “Electrodeposited composite coatings for protection from high temperature corrosion” in Trans IMF 1987, 65, 21 ff, V. Sova describes an electrolytic deposition process in which particles which are undissolved in the electrolyte are used for the layer which is to be applied. The use of pulsed currents is also described.

Under the conditions of some intended uses, layers applied with the known processes have poor bonding with respect to the substrate. Moreover, it is only possible to deposit materials of a constant composition.

Therefore, it is an object of the invention to overcome the abovementioned problems.

The object is achieved by an electrolytic process for depositing a graduated layer on a substrate as claimed in claim 1 and a component as claimed in claim 21.

The variation in the composition of the electrolyte over the course of time in order to produce graduated layers improves the bonding of layers to the substrate and if appropriate to one another, since abrupt transitions in the material can be avoided.

Further advantageous configurations of the process and of the component are listed in the subclaims. The process steps of the subclaims and the measures aimed at improving the component can advantageously be combined with one another.

Exemplary embodiments of the invention are explained in more detail in the figures, in which:

FIG. 1 shows an apparatus with which the process according to the invention can be carried out,

FIG. 2 shows a sequence of current/voltage pulses which can be used for a process according to the invention,

FIG. 3 shows the profile of the process according to the invention over the course of time,

FIGS. 4 a,b,c show various examples for a gradient layer,

FIG. 5 shows a gas turbine, and

FIG. 6 shows a combustion chamber.

FIG. 1 diagrammatically depicts, by way of example, an apparatus 1 which can be used to carry out the process according to the invention. An electrolyte 7, an electrode 10 and a component as substrate 13 that is to be coated are arranged in a vessel 4.

The substrate 13 that is to be coated is, for example, a turbine component (turbine blade or vane 120, 130 (FIG. 5), a combustion chamber lining 155 (FIG. 6) or another housing part of a steam or gas turbine 100 (FIG. 5)) made from an iron-, nickel- or cobalt-base superalloy and may already have a layer (MCrAlX) on its surface.

The component 13 may either be newly produced or refurbished. Refurbishment means that components, after they have been used, are if appropriate separated from layers (thermal barrier coating), and corrosion and oxidation products are removed, for example by an acid treatment (acid stripping). Cracks may also have to be repaired. Then, a component of this type can be coated again. Refurbishment is of economic interest since the substrate 13 is very expensive.

The substrate 13 and the electrode 10 are electrically conductively connected to a current or voltage source 16 via electrical supply conductors 19. The current or voltage source 16 can generate pulsed electric currents or voltages (FIG. 2).

The electrolyte 7 contains, by way of example, the individual constituents 28, 31 of an alloy which are to be deposited on the substrate 13. For example, the electrolyte 7 contains the first constituent 28 and the second constituent 31 of an alloy. The constituents 28, 31 are deposited on the substrate 13 by suitable selection of the process parameters (FIG. 2). The constituents 28, 31 may be metallic and/or ceramic. It is also possible for all the constituents to be only metallic or only ceramic.

It is also possible for gradients in the chemical composition to be produced in the layer that is to be produced, by suitable selection of the process parameters. By way of example, an alloy MCrAlX is deposited on the substrate 13, M standing for at least one element selected from the group consisting of iron, cobalt or nickel. The alloying elements Cr, Al, X and optionally further elements are introduced either by the addition of suitable soluble salts to the electrolyte or by the suspension of fine-grained, insoluble powders in the electroplating bath, which are deposited as solid particles. By way of example, at least two constituents are dissolved in the electrolyte 7, for example in the form of salts.

A subsequent thermal process allows the deposited layer to be homogenized or densified or allows specific phases to be set in the layer.

An ultrasound probe 22, which may be arranged in the electrolyte 7 and is controlled by an ultrasound emitter 25, improves the hydrodynamics and the mixing of the constituents 28, 31 in the region of the substrate 13 and accelerates the deposition process.

The current/voltage level, the pulse duration and the pulse interval can be defined for each constituent 28, 31 of the alloy.

FIG. 2 shows an example of a sequence of current pulses which are repeated. A sequence 34 comprises at least two blocks 37. Each block 37 comprises at least one, in particular two or more, current pulses 40. A current pulse 40 is characterized by its duration t_(on), its level I_(max) and its shape (square-wave, delta, etc.). Other important process parameters are the intervals between the individual current pulses 40 (t_(off)) and the intervals between the blocks 37.

The sequence 34 comprises, for example, a first block 37 of three current pulses 40, between each of which there is an interval. This is followed by a second block 37, which has a higher current level and comprises six current pulses 40. After a further interval, there follow four current pulses 40 in the opposite direction, i.e. with a reversed polarity, in order to correct the alloy composition, the hydrogen desorption or to achieve activation.

The sequence 34 is finished by a further block 37 of four current pulses. The sequence 34 can be repeated a number of times and can also be varied over the course of time.

The individual pulse times t_(on) are preferably of the order of magnitude of approximately 1 to 100 milliseconds. The time duration of the block 37 is of the order of magnitude of up to 10 seconds, so that up to 5 000 pulses are emitted in one block 37.

The application of a low potential (base current) both during the pulse sequences and during the intervals is optionally possible. This avoids interruption to the electrodeposition, which may cause inhomogeneities.

The parameters of a block 37 are matched to a constituent 28, 31 of the alloy, in order to optimize the deposition of this constituent 28, 31. This can be determined in individual tests. An optimized block 37 leads to optimized deposition of the constituent optimized for this block 37, i.e. the duration and nature of the deposition are improved. However, the other constituents are also deposited.

This optimization can be carried out for at least one further constituent, for example all the constituents 31, of the alloy. This results in an optimized composition of the constituents 28, 31.

The proportion of the constituents 28, 31 in the layer that is to be applied can be defined, for example, by the duration of the individual blocks 37. Gradients can also be produced in the layer. This is achieved by correspondingly lengthening or shortening the parameters of the block 37 which is optimally matched to a constituent 28, 31.

It is also possible for further nonalloy constituents, such as for example secondary phases, to be contained in the electrolyte 7 and deposited.

FIG. 3 shows the profile of the process according to the invention over the course of time. The apparatus 1 has an electrolyte 7, the first constituent 28 of which is, for example, metallic and has a composition MCrAlX.

The constituents 28, 31 of the electrolyte 7 are understood to be particles, dissolved salts, if appropriate with the addition of wetting agents or additives, which result in the constituents 28, 31 in the layer that is to be produced. An MCrAlX layer is electrolytically deposited on the component 13 in a known way. Over the course of time, at least one second, further constituent 31 is fed into the vessel 4 and to the electrolyte 7, and its concentration is increased, so that the composition of the electrolyte 7 changes. This can take place in one step or alternatively the concentration of the constituent 13 is continuously increased over the course of time, so that the percentage concentration of the first constituent 28 decreases. In this way, the composition of the electrolyte 7 is varied over the course of time. Therefore, the component 13 does not have to be introduced into different vessels 4 holding different electrolytes 7. The second constituent 31 may also be present in the electrolyte 7 from the outset and its concentration can then be increased further. It is also possible to vary the concentration of wetting agents and further additives.

If appropriate, in addition to the addition of the constituent 31, it is also possible for the composition of the electrolyte 7 to be varied by means of an outlet valve 40 through which electrolyte 7 containing the constituent 28 is discharged, so that as a result the concentration of the further constituent 31 in the electrolyte 7 likewise rises.

The further constituent 31 is likewise deposited, resulting in a layer which is graduated according to the increase in the concentration of the constituent 31. The graduated layer is a composite material. At the start of the process, a matrix is formed comprising the constituent 28, and this matrix contains the secondary phase 31, the proportion of which within the matrix may vary.

The proportion of the constituent 31 can also be increased by, in an inverse arrangement, the matrix being formed by the constituent 31 and the secondary phase being formed by the constituent 28.

FIG. 4 shows, by way of example, layer systems which can form as a result of the variation in the composition of the electrolyte 7 over the course of time.

FIG. 4 a shows a substrate 50 on which a layer 53 has been electrolytically deposited.

In a first process step, only the constituents 28 were deposited, as has been explained in connection with the first process step in FIG. 3. A layer 54, the composition of which comprises only the constituent 28, is formed. In a further process step, the concentration of the further constituent 31 was increased in a step, so that the material composition of the layer 55 to be deposited changes. Therefore, a further layer 55, which includes the constituents of the electrolyte 7 comprising the constituents 28, 31, is formed on the layer 54. A layer system 53 is formed.

Graduated layers can also be produced by continuously increasing the addition of the constituent 31 in the electrolyte 7 over the course of time t or discharging the electrolyte 7 comprising the constituent 28. The result, therefore, by way of example, is a layer as illustrated in FIG. 4 b. Once again, initially only a layer which results from the constituent 28 of the electrolyte has been formed on the substrate 50. A continuous or discontinuous increase in the constituent 31 in the electrolyte 7 over the course of time causes the concentration (c31) of this constituent 31 in the layer 55 to increase toward the outside.

However, it is also possible for the constituent 31 to be added to the electrolyte 7 from the outset, so that a concentration gradient is formed starting directly from the substrate 50.

FIG. 4 c shows a further layer system 53, which has been produced using the process according to the invention. The layer system 53 has multiply graduated layers 54, 55. For example, in a first layer 54 on the substrate 50, the concentration of the material of the substrate 50 decreases in the outward direction to a defined level, in this case zero, by the end of the layer 54 or earlier. At the same time, the concentration of the constituent 28 of the first layer 54 rises. After the concentration of the constituent 28 has reached 100%, for example, the concentration of the constituent 28 decreases again in the second layer 55. The concentration of the constituent 28 can drop to zero or a value other than zero. At the same time, the concentration of the constituent 31 in the layer 55 rises accordingly.

The substrate 50 consists, for example, of an iron-, nickel- or cobalt-base superalloy, the layer 54 may be an MCrAlX layer to which a ceramic thermal barrier coating 55 (ZrO₂) has been applied.

The concentration of the constituents 28, 31 may in addition also be influenced by varying the deposition parameters, such as current density, voltage, pulse duration and interval duration, by these parameters of the current/voltage pulses being specifically matched to the deposition properties of the constituents 28, 31.

FIG. 5 shows a longitudinal section through part of a gas turbine 100.

In the interior, the gas turbine 100 has a rotor 103 which is mounted such that it can rotate about an axis of rotation 102. An intake housing 104, a compressor 105, a, for example, toroidal combustion chamber 110, in particular an annular combustion chamber 106, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust-gas housing 109 follow one another along the rotor 103. The annular combustion chamber 106 is in communication with an, for example, annular hot-gas duct 111. There, by way of example, four series-connected turbine stages 112 form the turbine 108. Each turbine stage 112 is formed from two rings of blades or vanes. As seen in the direction of flow of a working medium 113, a row 125 formed from rotor blades 120 follows a row 115 of guide vanes in the hot-gas duct 111.

The guide vanes 130 are secured to the stator 143, whereas the rotor blades 120 of a row 125 are mounted on the rotor 103 by means of a turbine disk 133. A generator or working machine (not shown) is coupled to the rotor 103.

While the gas turbine 100 is operating, the compressor 105 sucks in air 135 through the intake housing 104 and compresses this air. The compressed air provided at the turbine-side end of the compressor 105 is fed to the burners 107, where it is mixed with a fuel. The mixture is then burnt so as to form the working medium 113 in the combustion chamber 110. From there, the working medium 113 flows along the hot-gas duct 111 past the guide vanes 130 and the rotor blades 120. The working medium 113 expands at the rotor blades 120, transferring its momentum, so that the rotor blades 120 drive the rotor 103 and the latter drives the working machine coupled to it.

While the gas turbine 100 is operating, the components which are exposed to the hot working medium 113 are subject to thermal loads. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, as seen in the direction of flow of the working medium 113, and also the heat shield bricks which line the annular combustion chamber 106, are subject to the highest thermal loads. In particular, they have a substrate, a directional structure, i.e. they are single-crystalline (SX) or longitudinally directed (directionally solidified (DS) structure). To withstand the temperatures prevailing there, they are cooled by means of a coolant. It is also possible for the blades and vanes 120, 130 to have coatings protecting against corrosion (MCrAlX; M=Fe, Co, Ni, X═Y, rare earths) and heat (thermal barrier coating, for example of ZrO₂ or Y₂O₄-ZrO₂ in the form of columnar grains (EB-PVD)), which are graduated and are produced using the process described above.

The guide vane 130 has a guide vane root (not shown here) facing the inner housing 138 of the turbine 108 and a guide vane head on the opposite side from the guide. vane root. The guide vane head faces the rotor 103 and is fixed to a securing ring 140 of the stator 143.

FIG. 6 shows a combustion chamber of a gas turbine. The combustion chamber 110 is designed, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners 102, which are arranged around the turbine shaft 103 in the circumferential direction, open out into a common combustion chamber space. For this purpose, the overall combustion chamber 110 is designed as an annular structure which is positioned around the turbine shaft 103.

To achieve a relatively high efficiency, the combustion chamber 110 is designed for a relatively high temperature of the working medium M of approximately 1 000° C. to 1 600° C. To allow a relatively long operating time even at these operating parameters, which are unfavorable for the materials, the combustion chamber wall 153 is provided, on its side which faces the working medium M, with an inner lining formed from heat shield elements 155. On the working medium side, each heat shield element 155 is equipped with a particularly heat-resistant protective layer, which can be produced in accordance with the invention, or is made from material which is able to withstand high temperatures. Moreover, on account of the high temperatures in the interior of the combustion chamber 110, a cooling system is provided for the heat shield elements 155 and/or for their holding elements.

The combustion chamber 110 is designed in particular to detect losses in the heat shield elements 155. For this purpose, a number of temperature sensors 158 are positioned between the combustion chamber wall 153 and the heat shield elements 155. 

1-22. (canceled)
 23. An electrolytic process for depositing a composite material on a substrate, comprising: introducing the substrate into an electrolyte containing a first constituent; electrolytically depositing the first constituent on the substrate to create a first layer; introducing a second constituent into the electrolyte; electrolytically depositing the second constituent on the first layer to create a second layer; varying a concentration of the fist and second constituents of the electrolyte to achieve a graduated layer; and using a current/voltage pulse to cause the electrolytic deposition such that an optimized deposition of the constituents occurs.
 24. The process as claimed in claim 23, wherein the substrate is arranged in a vessel filled with the electrolyte and the variation in the composition of the electrolyte during the period of time is effected by feeding the constituents into the vessel.
 25. The process as claimed in claim 23, wherein the substrate is arranged in the vessel and the variation in the composition of the electrolyte during the period of time is effected by the electrolyte comprising the first constituent such that the first constituent is partially removed and the second constituent being supplied.
 26. The process as claimed in claim 23, wherein the first constituent is metallic.
 27. The process as claimed in claim 23, wherein the first constituent is an alloy.
 28. The process as claimed in claim 23, wherein in the first constituent is a ceramic.
 29. The process as claimed in claim 23, wherein the second constituent is a ceramic.
 30. The process as claimed in claim 23, wherein the second constituent is metallic.
 31. The process as claimed in claim 23, wherein the electrolyte is mechanically vibrated by an ultrasound probe.
 32. The process as claimed in claim 23, wherein the current/voltage pulse and a time profile are used for the electrolytic deposition.
 33. The process as claimed in claim 23, wherein positive and negative current/voltage pulses are used for the electrolytic deposition.
 34. The process as claimed in claim 23, wherein a plurality of current/voltage pulses are combined in a sequence and are used for the electrolytic deposition.
 35. The process as claimed in claim 34, wherein the sequence comprises different blocks and a block comprises a plurality of current pulses.
 36. The process as claimed in claim 35, wherein the block is defined by a number of current pulses, a pulse duration, a pulse interval, a current level, and a time profile.
 37. The process as claimed in claim 35, wherein the block is matched to the first or second constituent of the alloy to optimize the deposition of the constituent.
 38. The process as claimed in claim 35, wherein the block is matched to the first or second constituent of the alloy to achieve the optimum composition of the constituents.
 39. The process as claimed in claim 23, wherein the layer deposited on the substrate is an MCrA1/X alloy, where M is an element selected from the group consisting of iron, cobalt or nickel, and X is yttrium, or at least one rare earth element.
 40. The process as claimed in claim 38, wherein an alloy layer that is produced and gradients in the material composition are influenced by a variation in the current/voltage pulse or the sequence during the period of time.
 41. The process as claimed in claim 23, wherein a base current is superimposed on the current pulses and the intervals.
 42. The process as claimed in claim 23, wherein a base current is superimposed on the current pulses or the intervals.
 43. The process as claimed in claim 23, wherein the substrate is a component of a steam turbine or a gas turbine.
 44. The process as claimed in claim 43, wherein the substrate is a component having no service history or a refurbished component.
 45. The process as claimed in claim 23, wherein the current/voltage pulse to cause the electrolytic deposition creates an optimized deposition of the constituents occurs.
 46. A coated turbine component, comprising: a substrate; a first layer comprised of a first constituent electrolytically deposited on the substrate; a second layer comprised of a second constituent electrolytically deposited on the first layer; and a graduated layer between the first and second layer produced by varying the concentration of the first and second constituent with the largest concentration of the first constituent toward the substrate and the largest concentration of the second constituent toward the second layer.
 47. The component as claimed in claim 46, wherein a first graduated layer of a first material is applied to the substrate and a second graduated layer is applied to the first graduated layer, the concentration of the first material decreasing in the layer starting from the substrate.
 48. The component as claimed in claim 46, wherein the concentration of the substrate in the first graduated layer decreases and the concentration of the first material in the first graduated layer increases. 